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<body>
<h3>1.规划异常</h3>
<pre><code>
考虑当前的功能可能会抛出哪些异常！
创建2个异常类
    com.abc.service.ex.UsernameDuplicateException
    com.abc.service.ex.InsertException
另外还需要创建这2个异常类公共的父级异常类
    com.abc.service.ex.ServiceException
它们都应该是 RuntimeException 的子孙类：
    并自动生成 RuntimeException 类的构造方法
</code></pre>
<h3>2.接口与抽象方法</h3>
<pre><code>
在设计业务层时，应该先有业务层的接口，并在接口中定义抽象方法，后续，外界(当前Model以外，例如Controller或其它Service等)调用时，是基于接口来声明对象，并调用方法的，所以，此处使用接口是一种解耦的做法！

先创建 com.abc.service.IUserService 业务层接口，并添加抽象方法：
    void reg(User user) throws UsernameDuplicateException, InsertException;
关于业务层的抽象方法的设计原则：

返回值：仅以操作成功为前提来设计返回值；

方法名：尽量体现业务，例如使用reg或regist或register表示注册，使用login表示登录；

参数列表：一定是客户端可以提供的数据，或来自于Session中的数据，且足够调用持久层的各方法；

异常：把用户操作失败的可能，都设计出各种异常，并把这些异常都添加到方法的声明中。
</code></pre>
<h3>3.实现类与重写方法</h3>
<pre><code>
创建 com.abc.service.impl.UserServiceImpl 业务层实现类，实现以上 IUserService 接口，添加 @Service 注解
里面模仿可能产生异常
</code></pre>
<h3>4.处理异常</h3>
<pre><code>
在编写处理请求的控制器及方法之前，还应该对异常进行统一处理！

首先，需要创建响应结果的数据类型 com.abc.util.JsonResult

在统一处理异常时，相关代码只能作用于当前控制器类，为了使得整个项目都可以使用这个统一处理异常的机制，
应该把相应代码添加在控制器类的基类 com.abc.controller.BaseController 中，代码如下：
</code></pre>
<pre><code>
@ExceptionHandler({ServiceException.class})
public JsonResult&lt;Void&gt; handleException(Throwable e) {
    JsonResult&lt;Void&gt; jr = new JsonResult<>();
        jr.setMessage(e.getMessage());

        if (e instanceof UsernameDuplicateException) {
            // 4000-用户名冲突异常，例如注册时用户名已经被占用
            jr.setState(4000);
        } else if (e instanceof InsertException) {
            // 5000-插入数据异常
            jr.setState(5000);
        }
    return jr;
}
</code></pre>
<h3>5.处理请求</h3>
<pre><code>
需要事先规划用户的请求是什么样的，例如用户向哪个URL发出请求表示“注册”，请求方式是哪种，是否需要提交某些请求参数等，以及最终服务器端向客户端响应什么样的数据：
请求路径：/users/reg
请求参数：User user
请求类型：POST
响应数据：JsonResult&lt;Void&gt;
创建 com.abc.controller.UserController 控制器类，继承自 BaseController
添加 @RestController 和 @RequestMapping("/users") 注解，
并在类中添加 @Autowired private IUserService userService; 业务层对象，并在类中添加处理请求的方法
</code></pre>
<pre><code>
@RequestMapping("/reg")
public JsonResult&lt;Void&gt; reg(User user) {
    // 执行注册
    userService.reg(user);
    // 返回成功
    JsonResult&lt;Void&gt; jr = new JsonResult&lt;Void&gt;();
    jr.setState(1);
    return jr;
}

</code></pre>








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